Dehydrogenation in the presence of oxygen and bismuth tungstate



Unite States Patent C 2,991,322 DEHYDROGENATION IN THE PRESENCE OF OXYGEN AND BISMUTH TUNGSTATE Warren E. Armstrong, Lafayette, Hervey H. Voge, Berkeley, and *Charles R. Adams, Oakland, Calif., assignors to Shell Oil Company, a corporation of Delaware No Drawing. Filed Dec. 29, 1959, Ser. No. 862,471 9 Claims. (Cl. 260-680) to olefin mole ratios as low as 1 to 1, it, is well known that much higher ratios are required for eflicient operation. In commercial practice this ratio is above at least 8 to l and generally around 12 to 1.

In the hitherto used commercial process quite high reaction temperatures are required. The range used commercially generally falls between about 1090 and 1200 F. At these high temperatures an in the presence of the large amounts of steam the activity of the catalyst is maintained by the continuous removal of carbonaceous deposits from the catalyst by the steam-carbon reaction which is catalyzed by the potassiumv carbonate in the catalyst. Thus the potassium carbonate is an essential ingredient.

An important factor in the production of butadiene and/or isoprene by dehydrogenation is the selectivity of the dehydrogenation process. The percent selectivity is defined as 100 times the moles of desired product produced divided by the moles of feed stock destroyed or otherwise converted. In order to obtain a reasonable selectivity the prior commercial process requires the use of low pressures. Generally pressures between about 5 and 25 p.s.i.a. are used. This necessitates large equipment and complicates the recovery of the product. At these low pressures and under otherwise near optimum conditions, a selectivity around 80% may be obtained at a total conversion around 20% in the dehydrogenation of butylene to butadiene. The operations are sometimes conducted under conditions of temperature and space velocity to obtain conversions as high as about 35%, but generally somewhat lower conversions are pre ferred because the selectivity drops sharply as the conversion is increased. Thus, one of the major shortcomings of the hitherto used process is that the conversion must be limited to quite low values (about 25%) and this requires the working up of large amounts of material to recover the product and requires a sizeable recycle which further increases the size of the equipment.

The object of the present invention is to provide a new and improved process for the catalytic dehydrogenation of normal butylene, isoamylenes (methylbutenes), and similar higher olefins having up to 6 or 7 carbon atoms to the cor-responding diolefins which process has one or more of the following advantages:

l) The process may be operated with no added steam while still retaining the activity of the catalyst at a high level.

(2) The process may be operated at relatively low temperatures (650ll00 F.). Whereas it is important to quickly quench the reaction product from the quite high reaction temperature to a safe temperature in the hitherto used commercial process, this is not essential in g the process of the present invention where lower temperatures can be used.

(3) Potassium carbonate is not an essential ingredient in the catalyst and in fact its presence is not recommended. Consequently difficulties due to hygroscopicity of the catalyst are avoided.

(4) The process may be eifected at comparatively high pressures thereby allowing small equipment to be used and facilitating the recovery of the product.

(5) The process may be operated at high conversions without sacrifice of the selectivity. This last is considered the most important of the advantages mentioned.

In general outline these objects are obtained by the process of this invention in which process a vaporized feed stream containing the olefin reactant to be dehydrogenated is passed together with certain specified amounts of oxygen and, if desired, a small amount of steam at temperatures between about 750 and 1000 F. over a bismuth tungstate catalyst and the vaporous efliuent is treated in appropriate ways to recover the conjugated diolefin as the major reaction product.

The process of the present invention is principally of value at present for the dehydrogenation of normal butylenes to butadiene and/or isoamylenes to isoprene but it can also be used to dehydrogenate normal amylenes to piperylene and higher olefins, e.g., hexenes and heptenes, to the corresponding more unsaturated products. The normal butylene may be butene-l or butene-2, either cis or trans, or a mixture of normal butylenes such, for example, as can be separated from the products obtained in the cracking of petroleum oils or by the catalytic dehydrogenation of normal butane. The isoamylene may be any one or a mixture of the methylbutenes (2,- methyl-l-butene, 3-methyl-l-butene, Z-methyl-Z-butene). The feed stock may contain inert diluents such as any parafiinic or naphthenic hydrocarbon having up to about 10 carbon atoms. Propylene and'isobutylene should, however, not be included in any substantial amounts i.e., not more than a few percent at most.

The feed stock may be catalytically dehydrogenated in the presence of added steam, but it is to be emphasized that the presence of added steam is only a small benefit and is not essential. Recommended proportions of steam are between about 0.1 to 2 moles per mole of reactant, but as indicated, larger amounts can be used if desired and, on the other hand, steam can be altogether omitted.

In the process of the present invention a certain amount of oxygen is passed with the feed stock through the reaction zone. Recommended amounts are between about 0.3 and 2.0 moles per mole of olefin reactant. The stoichiometric quantity to react with the hydrogen removed is around 0.4 moles per mole of olefin depending on the extent of conversion. It is preferred to use a stoichiometric excess e.g., around 0.5 to 1 mole per mole of olefin. The oxygen may be supplied as pure or substantially pure oxygen, or diluted oxygen, e.g., air.

It is generally preferred to maintain the concentration of oxygen in the reactant mixture entering the reactor below about 12 v. percent although somewhat higher concentrations may be used if the concentration of the olefin reactant is at least about 10 v. percent when operating at 30 p.s.i.g., at least 15 v. percent when operating at p.s.i.g. and at least about 20 v. percent when operating at 300 p.s.i.g. Thus, when using pure oxygen it is frequently desirable to dilute the mixture with an inert or substantially inert diluent which may be steam, N vapors of paraflin hydrocarbons, CO or the like. On the other hand, if the amount of oxygen is such that it would constitute more than about 12 v. percent of the reaction mixture the oxygen may be introduced in increments e.g., by injecting part of the oxygen separately into the reaction zone.

The catalyst used in the process of the invention is bismuth tungstate, nominally Bi W O It contains no potassium carbonate or the equivalent thereof and the process does not depend upon the steam-carbon reaction to maintain catalyst activity. Nevertheless continuous operation is possible. While the catalyst is bismuth tungstate the bismuth and tungstate need not be present in the catalyst in a 2:3 atomic ratio. As the atomic ratio of bismuth to tungsten is increased above 2:3 the activity of the catalyst declines but ratios up to about 2:1 can be used. On the other hand, ratios as low as 1:4 are suitable.

The catalyst may be prepared from any of thesoluble bismuth salts such as nitrate or the like. Water soluble salts of tungsten such as ammonium tungstate can be used to supply the tungsten. We prefer, however, to supply the tungsten in the form of one of the heteropolyacids of tungsten such as phosphotungstic acid, silicotungstic acid and their soluble salts. Thus, the catalyst may contain in addition to the bismuth and tungsten up to about 1 atom of phosphorous or silicon per 12 atoms of tungsten.

Any suitable method may be used in preparing the catalyst. For example, bismuth nitrate and ammonium tungstate may be kneaded together with a little water to form a paste. After drying the material is calcined at about 500 C. and the resulting cake is broken up into pieces of convenient size. In another suitable method an acidic solution of bismuth nitrate is mixed with a solu tion of phosphotungstic acid and the mixture neutralized with ammonium hydroxide. The resulting precipitate is washed, partly dried, kneaded with a few percent of a silica sol and the material is then dried, calcined, and crushed as before.

The catalyst may be used with or without a filler or carrier material. If a carrier is used it is preferably one having a relatively large volume of pores of relatively large size, such, for instance, as pellets of Alundum (a bonded form of corundum), crushed fire brick, pumice, sintered or bonded silica sand aggregates, or the like. A relatively inert filler or binding agent in an amount up to about 50% by the weight of the total may be included. Suitable materials are, for example, colloidal silica, ball clay, and the like. The carrier, if used, may be impregnated with the bismuth tungstate by precipitating the bismuth tungstate in the presence of a powdered carrier or, for instance, by impregnating the carrier first with an acidic solution of bismuth acetate or an ammoniacal solution of bismuth citrate or lactate, drying and calcining in air followed by impregnating with a solution of silico-tungstic acid and again drying and calcining at around 900 F. During preparation and use of the catalyst it should not be subjected to temperatures above about 1300 F. and preferably not above 1200" F.

The dehydrogenation becomes substantial at a minimum temperature around 650 F. The preferred temperatures are between about 750 and 1100 F. Higher temperatures up to about 1200 F. can be used, but only if efficient means are provided to remove the exothermic heat of reaction. The temperatures mentioned are those near the reactor inlet. If a fixed bed of catalyst is used the temperature down stream may be considerably higher, e.g. 150 F. higher.

The preferred pressure is near atmospheric e.g., 5 to 75 p.s.i.a. On the other hand, higher pressures up to about 300 p.s.i.a. can be used and have the advantage of simplifying the product recovery.

In general the process of the present invention allows a high space velocity to be used. Thus, comparatively small reactors and catalyst inventories can be used. For example, gaseous hourly space velocities up to about 3,000 may be employed while still obtaining reasonable conversions. Gaseous hourly space velocity, abbreviated GHSV, is defined as the volumes of hydrocarbon reactant vapor calculated under standard condition (STP) passed per hour per unit volume of the catalyst bed. A wide range of space velocities may be used. Generally space velocities between about 50 and 1,000 are very satisfactory.

The contact of the feed vapors, oxygen, and steam, if any, is preferably effected by providing the catalyst in the form of a fixed foraminous bed of particles maintained at the reaction temperature and passing the feed vapors through the bed in a continuous or substantially continuous manner. In this method of operation the partial pressure of oxygen is high (maximum) at the inlet of the catalyst 'bed and declines towards the outlet. The concentration of diolefin product, on the other hand, is substantially zero at the inlet of the bed and maximum at the outlet. Thus, the concentration of oxygen is highest where the concentration of the desired product is lowest and the concentration of oxygen is lowest where the concentration of the desired product is highest. It is also possible to use the catalyst in powder form. Thus, the powdered catalyst (e.g., passing a mesh U.S. standard sieve) can be dispersed in the reactant vapor mixture and the dispersion passed through the reaction zone. Alternatively the reactant vapor mixture may be passed up through a fluidized bed of the catalyst. In this case the oxygen may be separately introduced into the catalyst bed.

The gaseous mixture issuing from the reaction zone may be quenched but this is normally not essential. Except in some cases when operating at the upper limit of the recommended temperatures there is little tendency for side reactions to take place. The effluent is preferably cooled by indirect heat exchange with the feed and then washed with dilute caustic to neutralize the traces of organic acid present and condense and remove the steam. If air is used to supply the oxygen the remaining mixture is preferably compressed and scrubbed with oil to separate the hydrocarbons from the nitrogen, carbon dioxide, and carbon monoxide and any unreacted oxygen. The hydrocarbon may be stripped from the oil and subjected to an extractive distillation or a copper ammonium acetate treatment in the known manner to separate and recover the diolefin.

Example I A catalyst was prepared by preparing an aqueous solution of ammonium tungstate and an aqueous solution of nitric acid and bismuth nitrate. The former solution was added to the latter. A white precipitate was formed. The pH of the slurry was then raised from 1.2 to 5.95 by the addition of ammonium hydroxide. The bismuth tungstate having an atomic ratio of Bi/W of about 1:1 was filtered, washed, dried at C., calcined for about 2 hours at 500 C. and broken up into 10 mesh particles.

This catalyst was tested for the dehydrogenation of n-butylene to butadiene. The n-butylene was mixed with an equal molar amount of oxygen and diluted with about 4 parts of inert gas and the gas mixture passed over the catalyst at atmospheric pressure, a butenes gaseous hourly space velocity of 600, and a temperature of 470 C. Analysis of the product showed that under these conditions 66% of the butylene was converted and 78% (molal) of that converted was found in the product as butadiene.

Example II A catalyst was prepared in the same general manner as in Example I except the ratio of Bi to W was 2:3. When the solutions were mixed the pH of the resulting slurry was 7.7 and no additional ammonium hydroxide was required. The catalyst was worked up in the same manner. The catalyst was a pale yellow in color.

Example III A catalyst containing B, P and W in the atomic ratios of 12:1:12 was prepared by adding a solution of phosphotungs-tic acid to a solution of bismuth nitrate and adding ammonium hydroxide to a final pH of 5.73. The precipitate was filtered, washed, dried, calcined and crushed in the manner before indicated.

This catalyst was tested as in Example I and found to give most excellent results. It was found also to be exceptionally stable and to give exceptional results at higherthan-usual temperatures. Thus, at 530 C. butadiene was produced with a selectivity of 86% at 84% conversion of the butylene.

We claim as our invention:

1. Process for the selective dehydrogenation of a monoolefin aliphatic hydrocarbon having from 4 to 7 nonquaternary contiguous carbon atoms to produce as the major reaction product a hydrocarbon having the same number of carbon atoms but at least one more ethylenic bond which comprises passing the first said hydrocarbon in the vapor phase together with oxygen in a ratio of about 0.3 to 2.0 moles of oxygen per mole of monoolefin through a reaction zone in contact with a solid catalyst comprising a bismuth rtungstate as its main active constituent at a temperature between about 750 and 1100 F., a pressure between about 5 and 300 p.s.i.a., cooling the efiluent from said reaction zone, separating fixed gases from a liquid hydrocarbon phase and recovering said second mentioned hydrocarbon from said hydrocarbon phase.

2. The process according to claim 1 in which the atomic 6 ratio of bismuth to tungsten is between about 1 to 4 and 2 to 1.

3. The process according to claim 1 in which the atomic ratio of bismuth to tungsten is about 1:1.

4. The process according to claim 1 in which the said tungsten is incorporated in the catalyst in the form of a heteropoly acid of tungsten.

5. The process according to claim 1 wherein the catalyst is disposed as a fixed foraminous bed.

6. The process according to claim 1 which the dehydrogenation is efiected at substantially atmospheric pressure.

7. The process according to claim 1 in which the oxygen is supplied as 8. The process according to claim 1 in which the first said hydrocarbon is a normal butylene and the second said hydrocarbon is butadiene.

9. Process for the selective catalytic dehydrogenation of a monoolefin having from 4 to 7 nonquaternary carbon atoms to a corresponding diolefin which comprises passing the said monoolefin in the vapor phase together with an approximately equal volume of oxygen through a reaction zone in contact with a bismuth tungst-ate catalyst at a temperature between about 750 and 1100 F. and a pressure between about 5 and 300 p.s.i.a.

References Cited in the file of this patent UNITED STATES PATENTS 

1. PROCESS FOR THE SELECTIVE DEHYDROGENATION OF A MONOOLEFIN ALIPHATIC HYDROCARBON HAVING FROM 4 TO 7 NONQUATERNARY CONTIGUOUS CARBON ATOMS TO PRODUCE AS THE MAJOR REACTION PRODUCT A HYDROCARBON HAVING THE SAME NUMBER OF CARBON ATOMS BUT AT LEAST ONE MORE ETHYLENIC BOND WHICH COMPRISES PASSING THE FIRST SAID HYDROCARBON IN THE VAPOR PHASE TOGETHER WITH OXYGEN IN A RATIO OF ABOUT 0.3 TO 2.0 MOLES OF OXYGEN PER MOLE OF MONOOLEFIN THROUGH A REACTION ZONE IN CONTACT WITH A SOLID CATALYST COMPRISING A BISMUTH TUNGSTATE AS ITS MAIN ACTIVE CONSTITUENT AT A TEMPERATURE BETWEEN ABOUT 750 AND 1100*F., A PRESSURE BETWEEN ABOUT 5 AND 300 P.S.I.A., COOLING THE EFFLUENT FROM SAID REACTION ZONE, SEPARATING FIXED GASES FROM A LIQUID HYDROCARBON PHASE AND RECOVERING SAID SECOND MENTIONED HYDROCARBON FROM SAID HYDROCARBON PHASE. 